With its superior hardness, transparency, thermal conductivity and chemical stability, diamond would be the material of choice for a vast array of components for tribological or high-stress optical applications. Applications range from relatively mundane tooling for machining of abrasive materials such as metal-matrix composites to windows and optical objectives for ultra-high velocity missiles and aircraft. Until recently, actual applications of diamond has been limited to those which may be satisfied by optically poor but relatively cheap sintered polycrystalline diamond compact (PCD) or sections cut from large, and therefore extremely expensive, diamond crystals. Such applications are further limited to shapes and configurations which may be produced from such "bulk" materials. Over the last decade, rapid advances in the technology of chemical vapor deposition (CVD) of diamond in the form of films and coatings has opened the range of diamond applications. Using the CVD methods an object of almost any shape may be coated with diamond so long as the material itself can survive the conditions required for diamond CVD. Some examples of new applications include high frequency loudspeakers, complex cutting tools, dies, drills, reamers and taps, X-ray transparent vacuum windows, abrasion resistant objectives for military optical systems and heat extraction for super-high density electronic circuits.
Although physical survival in the diamond growth environment is the primary criterion for a substrate suitable for diamond coating, a second criteria is that diamond nucleate on and adhere to the surface. Diamond nucleates most readily on diamond itself. Diamond also nucleates on cubic boron-nitride, which is even less available than diamond, and to a lesser extent some carbides (boron-carbide, silicon-carbide and tungsten carbide). Therefore, for most practical applications, some sort of pretreatment to promote diamond nucleation is necessary. Several methods for enhancing diamond nucleation have been demonstrated. These fall into three broad categories: (1) in-situ (meaning in the growth reactor) bombardment with hydrocarbon ions (as demonstrated by Stoner and Glass), (2) direct dispersal of find diamond grit by spray- or spin-coating (U.S. Pat. No. 4,925,701 or Massood et al. 1991), and (3) physical abrasion by diamond particles by mechanical contact (scratching or polishing) or bombardment by ultrasonic agitation of diamond grit suspended in a suitable fluid. The first appears to be limited to crystalline silicon substrates, while the second is suitable only for nearly flat or simply shaped objects. In the third category, physical scratching is also limited to simple shapes determined by the medium (e.g. sandpaper) which carries the diamond abrasive, is often inconsistent and can physically damage the substrate. The ultrasonic bombardment method has grown in popularity because it is gentler, suitable to virtually any substrate material or shape, and is very reproducible. In all published descriptions of this method we are aware of the suspending liquid has been described as simple water or a heavy alcohol, usually isopropanol. Although higher densities are occasionally reported, typical nucleation densities of the order 10.sup.8 nuclei/cm.sup.2 are generally obtained and are sufficient for many applications. However, if an extremely smooth, fine-grained film, or a very thin film free of microscopic pin-holes is desired, much higher densities must be achieved consistently. Furthermore, for some substrates an increased density of nuclei translates into superior film adhesion. It is desirable, therefore, to use a pretreatment process for enhancement of diamond nucleation which can readily produce 10.sup.11 nuclei/cm.sup.2 on a substrate of arbitrary shape and size without macroscopic damage. The present invention provides such a pretreatment method for diamond nucleation.